Methyl bromide is widely used for fumigating fruits, vegetables, grains, soil, lumber and enclosures requiring a sterilized atmosphere. However, methyl bromide is now recognized as a major ozone depleting substance (ODP) and will be regulated with other ODP substances under the Montreal Protocol. While its ODP potential of 0.7 is high, a major concern is its ability to achieve that potential in a much shorter time span than chlorofluorocarbons (CFCs), making it more potentially damaging to the ozone layer in the next ten years.
The current method of fumigating fruits and vegetables or other produce with methyl bromide is to fill a chamber defining an enclosed space of, e.g. 1000 ft.sup.3 to over 100,000 ft.sup.3 with the produce. Pure methyl bromide is added to the chamber at a concentration of 10,000 to 20,000 ppm and maintained for several hours to ensure proper fumigation. For example, when fumigating cherries, 65 g/m.sup.3 of methyl bromide is added to the chamber and maintained for 2 hours.
After the required time, the chamber is purged with huge amounts of fresh air and all the remaining methyl bromide is vented to the atmosphere. As only up to about 20% of the methyl bromide is actually consumed in the process, about 80% of the total methyl bromide must be vented to the atmosphere. In some cases, the methyl bromide is diluted with sufficient fresh air to attain a 500 ppm concentration in the effluent. In any event, no matter what the concentration, all of the unused methyl bromide must eventually be vented to the atmosphere.
Most fruit seasons are very short and it is economically valuable to shorten the cycle time to enable higher chamber utilization.
One purpose of the present invention is to prevent pollution of the atmosphere with methyl bromide during fumigation of a product.
Another purpose of the invention is to shorten the time between fumigation cycles.
A still further purpose of the invention is to recycle unused methyl bromide to the fumigation process.